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Feb. 1 1927. 1,616,414

c. A. CULVER MICROPHONE Fi led May 10, 1926 INVENTOR.

I A TTORNEY I transformer.

Patented Feb. 1, 1927.

UNITED 1,616,414 Parent series.

CHARLES A. CULVER, OF NORTHFIELD, afinnnse'ra, AS=SIGNOR .TO VIIRED RAZDZO, ENG,

OF NEW YORK, N. Y. A CORPORATION OF DELARVAEE.

MICROPHONE.

Application filed May 10,

My invention relates to an improved type of microphone whlch 1s designed partlcularly for use in connection with radio-broadcasting and public address systems.

One of the objects of my invention is to provide a n'iicrophone or pick-up device in which the customary vibratile diaphragm doesnot form an essential part or element in its construction and operation.

Another object of my invention is to provide means whereby the so-called carbon hiss is materially reduced.

Afurther object of my invention is to prevent packing of the granular material commonly used as an element in microphonic devices.

The invention will be understood by reference to the accompanying drawings in which: j V

Figure 1 illustrates a cross-sectional view through a microphone embodying the principles of my invention; Fig 2 is a cross-sectional view through a modified form of microphone construct-ion in accordance with the principles of my invention; and Fig. 3 shows a still further modification of the microphone construction of my invention. I

Figure 1 shows in cross section a preferred form of the invention. The body of the microphone designated as 1 in the drawing consists of a solid block of marble, glass, porcelain or other relatively heavy insulating material which forms a non-vibratile Orin and support for the several elements constituting the device. Two rectangular carbon mirrors, or other suitable electrodes 3 are securely attached to the body in recesses provided for that purpose in the cut out portion 2 in the block. Terminals l are attached to the electrodes 3 whereby the microphone may be connected in series with the usual source of potential and primary of a Granular microphonic material 5 occupies the V-shapedspace between the electrodes 3. Above the granular material, and also in the interstices between the particles of granular material, is placed a non-conducting liquid 6, such as chemically pure water, alcohol, or other similar liquid.

.The granular material 5 thus is immersed in'said liquid6 and is also covered by it. A thin layer of oil 7 prevents the evaporation of the water, alcohol, or other liquid 6 beneath.

Heretofore a vibratile diaphragm has been 1926. Serial No. 103,103.

utilized for the purpose of t 'ansterring the energyof the. incident sound waves to the electrodes or granular n'iaterial, or the sound waves have been caused to in ipinge directly upon the granular substance. In those devices of the former type it has been found necessary to subject the diaphragm to relatively high peripheral tension in order that the natural period of vibration of the dia by means of the liquid 6 which forms a part oi the device. As a result of the operation of Pascals principle the pressure due to the incident sound waves is transferred without loss to all of the granular material 5. Thus the total eifect of a sound wave is materially greater than would be the case if the liquid were not present. Experiment shows that the sound sensitivity of a microphone having a liquid 6 as one of its elements is several fold greater than one without that feature. I

Further, in any pick-up device employing such granular material as carbon the minute electric arcs formed between the particules of microphonic material give rise to what is known as the aarbon hiss which when amplified, produces a very undesirable background of extraneous sound. The presence of the nonconducting liquid in my invention inhibitsthe to mation of these minute arcs, thus materially reducing thecarbon hiss. The presence of the liquid also acts to prevent the packing of the granular material with attendant loss of sensitivity.

Figure 2 shows one of the practical forms of my invention. In this arrangement 8 designates a lower block member which is bridged across the top thereof by an upper block member ,9. The block members 8 and 9 are suitably united by means of screws 10. The recess 11 which is provided in the upper block portion 9 registers with a recess 12 in the lower block member which serves as a pocket or seat for a carbon ring memher 13 which surrounds a central carbon button or electrode 14. The ring member 18 and central carbon button 1% serve as opposite sides of the microphone and leads 15 and 16 extend therefrom. The granular conductive material 17 occupies the space between the carbon ring member 13 and the central electrode 1-1. This material is cov ered by the liquid 18 such as alcohol, which is in turn covered with a film of oil 19.

Figure 3 shows a.form of construction of my invention in which a deflecting surface 30 is utilized for the purpose of reflecting horizontally moving sound waves onto the liquid surface of the microphone proper. Such a type may be usedin connection with the transmission of speech and certain types of music.

In this figure I have shown a block 20 having a'recess 21 therein in the lower portion of which I mount at spaced intervals the carbon blocks 22 and 23 which connect through leads 2 1 and 25 to the control circuit. The space between the carbon mirrors and 23 is filled with the granular material 26 which is in turn covered by the liquid 27 having a film of oil 28 ther-eover. The deflecting surface 30 is secured adjacent one side of the block 20 by any suitable means. such as screws 29. This arrangement perinits the placing of the microphone on a vertical stand convenient to the broadcast artist or in a position where music maybe readily directed against the sensitive elements of the microphone.

I have found the construction of this invention highly sensitive in its operation, and while I have shown the invention in a num ber of its preferred embodiments, I desire that it be understood that modifications may be made and that no limitations upon the invention are intended other than are imposed by the scope of the appended claims.

lVhat I claim as new and desire to secure by Letters Patentof the United States is as follows:

1. A device for converting sound vibrations into variable electrical current which comprises an insulated block member. a pair of conductive electrodes mounted in said block member and substantially covered by conductive granular material, a pool of liquid covering said granular material and a film of oil on the surface of said liquid for providing a sound transmitting medium for effecting variations in pressure throughsaid granular material for varying the conductivity between said electrodes in flCCOltldIlCrwith sound vibrations.

2. A device for converting sound vibrations into variations of electrical current, the combination of an insulated body structure recessed to receive a pair of electrodes therein, a mass of granular particles substantially covering said electrodes and'a pool'of liquid over said granular particles for transmitting pressure effects derived from sound waves granular material arranged to substantially cover said electrodes, a pool of fluid in which said granular material is substantially immerseil, and means for directing sound waves against the surface of said pool of liquid for imparting variable pressure to said granular body for changing the electrical conductivity between said electrodes in accordance with sound vibrations.

4-. A device for converting sound vibrations into variable electrical current, comprising a horizontally extending insulated body structure recessed to receive a pair of electrodes, a body of granular material arranged to substantially cover said electrodes, a fluid body in which said material is arranged to be immersed, a sound deflecting surface secured to said body structure for directing sound waves incident thereon against said fluid body for creating variations in pressure through said granular material in accordance with variations in sound vibrations.

5. A device for converting sound vibrations into variable electrical current, comprising in combination an insulated body structure recessed to receive a pair of electrodes spaced apart and disposed at an angle with respect to each other, a body ofgranular material arranged between said electrodes, a fluid body siibstantially covering saidbody of granular material for receiving sound vibrations directed thereagainst and transmitting pressure ei'i'ects to said body of granular material for changing the electrical conductivity between said electrodes in accordance with variations in the amplitude of sound vibrations.

6. A device for converting sound vibra tions into variable electrical current, the combination of an insulated body structure having a substantially conical recess therein. a pair of electrodes spaced one from the other and arranged substantially in the form of a V, a body of. granular material arranged to substantially fill the space between said electrodes, a pool of fluid substantially covering said body of'granular material and arranged to receive sound vibrations and transmit the pressure effects thereof to said body of granular material for changing the electrical conductivity between said electrodes in accordance with sound vibrations.

In testimony whereof I affix my signature.

-CHARLES A. OU'LVER.

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